Pitfalls of assessment of autonomic function by heart rate variability

Fig. 1. Association between LF/HF and lying ratio during 24-h monitoring in 18,944 men and 23,539 women who underwent 24-h Holter ECG monitoring with tri-axial accelerogram to assess physical activity and body position. Data were obtained from 24-h long-term HRV database of the Allostatic State Mapping by Ambulatory ECG Repository (ALLSTAR) project. (Revised figure in reference [31])

Fig. 2. Schema of the effects of physiological RSA and its inversion (inverse RSA) on the relationship between alveolar gas volume and capillary blood flow during inspiration and expiration. Horizontal red bows and vertical green arrows indicate the volume of blood flow and the direction of gas flow, respectively. Physiological RSA improves respiratory gas exchange efficiency through matching between alveolar ventilation and capillary perfusion throughout the respiratory cycle, while the inversion of the relationship (inverse RSA) results in increased alveolar dead space (wasted ventilation) and increased intrapulmonary shunt. (Revised figure in reference [61])

Fig. 3. Model of central regulations RSA and the level of heart rate by preganglionic cardiac vagal motor neurons. RSA is generated by the phasic control system located in the nucleus ambiguous (nA) that regulates the amplitude of respiratory modulation of cardiac vagal outflow, while bradycardia is derived by the tonic control system located in the dorsal motor nucleus of the vagus (DVN) that regulates average cardiac vagal tone. These systems work independently of HRV of each other and are stimulated (solid arrows) or inhibited (broken arrows) by different kinds of inputs. However, both systems appear to work in parallel and to link with each other, whenever the cardiac autonomic state changes along with the rest-strain axis. (Revised figure in reference [61])